To sum up, I think its fair to say that although you certainly pay a small premium for this type of noise reduction technology, each one of the items looked at for this feature proved its worth to some extent. True, some reductions were greater than others but at the end of the day every little helps if your main objective is to eliminate the last remaining traces of noise from your PC.
Whether you choose to use all of these products or just pick one or two selective components will of course depend on your own particular set-up and budget. However, if you want a totally silent system, there are noiseless systems available such as the pricey Zalman TNN500 reviewed here.
Finally and most importantly, the last thing you want is a component or system failure due to over-heating. It goes without saying therefore, always be sure to test and monitor your system temperatures after installing any new products and if in any doubt, seek expert advice before modifying your existing PC.
Below is a table showing all the components we used for this test and their price at QuietPC. (Correct at the time of writing).